Two-way information transmission system, two-way information transmission method and subscriber terminal device

ABSTRACT

The subscriber terminal ms sends the demand including at least information for identifying the demand subscriber terminal, information for identifying the requested information, and information relating to the urgency of the requested information to the information distribution transmission center HE through an going-up line. The information distribution transmission center HE plans a transmission schedule of the information to be transmitted based on the demand from the subscriber terminal ms, and transmits the transmission schedule information included in the down-going control data to the subscriber terminal which sent the demand prior to the actual transmission, and transmits the requested information according to the above-mentioned transmission schedule. The subscriber terminal ms receives and analyzes the down-going control data from the information distribution transmission center HE and is informed of the transmission schedule, and acquires the information to be transmitted based on the obtained transmission plan, stores the acquired information in a large scale memory, and reads the information from the memory means for use. A video on-demand system can be realized without introducing a large scale system such as video server and with a relatively small investment, and the centralization of traffic is mitigated, and the network resource is used efficiently.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a two-way information transmission system suchas video on-demand system and information on-demand system using acommunication network such as cable television network.

2. Description of Related Art

Not only usual analog broadcasting service but also video on-demand,home shopping, and television game service utilizing a two-way cabletelevision network have been recently planned.

One method for realizing such services is a method in which a digitalinformation transmission band is provided, for example, in thetransmission band of the television network separately from the band foranalog broadcasting service. In detail, for example in the case of videoon-demand system, a user transmits a demand signal (transmission requestsignal) of the video on-demand to a cable television station where avideo program storing sending system called video server is installedusing a portion of the digital information transmission band. Uponreceiving the demand signal from the user, the cable television stationtakes out the program requested by the user from the video server, andprovides it to the requesting user in real time using a band other thanthat for the above-mentioned demand signal in the above-mentioneddigital information transmission band.

One of such video on-demand systems is introduced in a journal "NikkeiElectronics" issued May 23, 1994 on pages 82 to 89.

This example involves a hybrid network system comprising combinedoptical fiber and coaxial cable, the optical fiber connects from thecable television station to an optical fiber node, the optical fibernode performs photoelectric conversion, and the coaxial cable connectsfrom the optical fiber node to a subscriber terminal called as set topbox installed in the user home. Assuming that 16 optical fiber nodes areprovided and the maximum number of subscribers connectable to a coaxialcable is 500, then one cable television station can supply to 8000subscribers.

In assignment of transmission band of the cable television, This videoon-demand system assigns the band range from 50 MHz to 723 MHz to atransmission band for going-down from the cable television station to asubscriber terminal of a subscriber, and the band range from 900 MHz to1 GHz to a transmission band for going-up from a subscriber terminal tothe cable television station, further, a transmission band between 50MHz to 450 MHz out of the going-down transmission band is used for theexisting analog broadcasting service and a transmission band between 500MHz to 708 MHz is used for digital transmission band. and the residualtransmission band ranging from 450 MHz to 500 MHz is spare as shown inFIG. 1

At most 15 digital transmission channels with a band width of 12 MHz canbe provided in the digital information transmission band ranging from500 MHz to 708 MHz. Assuming that the transmission speed per one channelis 45 M bits/sec and, for example, the coding speed of video data is 4 Mbits/sec, video data can be supplied to about 10 subscribers by way of achannel with the transmission speed of 45 M bits/sec in real time.

Assuming that the proportion of requesting subscribers for demand to 500subscribers is 25% in the busy time called as prime time, it is requiredto supply to 125 subscribers, and one channel can supply to 10subscribers, therefore 15 channels can supply to 150 subscribers andthus the requirement is satisfied.

In the case of this example, the control channel is assigned near thefrequency of 500 MHz, and the going-down channel to be used forsupplying a video program data desired by a user through demand isinformed to the set top box using this control channel. The set top boxfetches only a desired going-down data in the cable television stationbased on the data of the control channel, and functions to display it ona television. The transmission speed of the control channel is 1.5 Mbits/sec, and 45 channels and 1 channel are for going-up and for goingdown respectively.

FIG. 2 shows how the transmission capacity of going-down line isallocated to respective subscribers, the left half of the figure showsso-called prime time and the right half shows the midnight time zone.

In FIG. 2, the top half shows the transmission channels for analogtelevision broadcasting service, each long rectangle represents oneanalog television program PGa. In this case, 50 channels of analogtelevision broadcasting service are possible to be transmitted if onechannel has a band width of 6 MHz. Each subscriber can select and view adesired program from programs being broadcasted by way of analogchannels any time.

The bottom half of FIG. 2 shows the digital information channels forvideo on-demand, an arrow Tdm represents a demand generating time pointfrom a user, and a long rectangle represents a one digital video programPGd. In response to a demand from a user, one channel is occupied by theuser for a time of the service.

In FIG. 2, rating is high for the analog broadcasting program and alsodemand generation rating is high for the digital video program in primetime, on the other hand, rating is low for the analog broadcastingprogram and also demand generation rating is low for the digital videoprogram in midnight.

As described hereinabove, in the conventional video on-demand system,video programs are supplied in real time to all the demands. Therefore,in the time zone like so-called prime time when many demands arerequested from subscribers, many programs should be transmitted at atime as shown in the left side of FIG. 2.

For construction of a video on-demand system, the network capacity andtransmission system are deployed so that programs are supplied tosubscriber homes as soon as possible in real time in the busiest timezone when many demands are requested.

To cope with such situation, the conventional system is involved in aproblem that 1 the network capacity should be large, and 2 the scale ofvideo server should be large in order to supply many programssimultaneously (for example, assuming the number of subscribers is 8000and 25% of these subscribers request their demand in prime time, thesimultaneous transmission stream are 2000 streams). The capacityinvestment for enlargement of an existing facility is required, and anexpensive large scale video server should be introduced, theseexpenditure can render the business substantially unprofitable.

As described herein above, many demands are generated very frequently inprime time, on the other hand, a few demand is generated sporadically inthe time zone of early morning and midnight, the problem is inefficientuse of the network facility having a large capacity deployed so as tomatch with busy demand in prime time, the capacity utilization ratio islow.

Further, the change of a cable television facility from existing one-waysystem to the above-mentioned two-way system requires the large scalereplacement of infrastructure due to the above-mentioned problem, theexpenditure for such investment is also very heavy and a problem.

It is the object of the present invention to provide a two-wayinformation transmission system for solving problems described hereinabove.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problem, the two-way informationtransmission system of the present invention is provided with; aninformation distribution transmission center and a plurality ofsubscriber terminals connected to the information distributiontransmission center through going-up lines and going-down lines, inwhich the subscriber terminal requests an information to the informationdistribution transmission center through the going-up line, and theinformation distribution transmission center transmits the requestedinformation in response to the request for the transmission; theinformation distribution transmission center having; transmissionplanning means for planning a transmission plan to transmit theinformation based on an information distribution transmission requestfrom the subscriber terminal, transmission implementation means forimplementing the transmission of the requested information based on thetransmission plan planned by the transmission planning means, andgoing-down control data sending means for sending a going-down controldata including an information involving the transmission implementationplan planned by the transmission implementation means to the subscriberterminal which sent the information distribution transmission requestbefore the transmission implementation means implements thetransmission, the subscriber terminal having; distribution transmissionrequest sending means for sending the information distributiontransmission request including at least information for identifying thedemand subscriber terminal, information for identifying the requestedinformation, and information relating to urgency of the requestedinformation, memory means, transmission plan receiving analysis meansfor being informed of the transmission plan based on the going-downcontrol data from the information distribution transmission center,information acquisition means for acquiring the information transmittedfrom the information distribution transmission center based on thetransmission plan and storing it in the memory means, which informationwas acquired by the transmission plan receiving analysis means, andreading means for reading the information from the memory means.

In the two-way information transmission system of the present inventionhaving the structure described herein above, the informationdistribution transmission center transmits the information to asubscriber terminal either in real time or at a desired delayed timedependently on a transmission plan planned based on the information ofthe information use time desired by the subscriber included in thetransmission request from the subscriber terminal. The subscriberterminal stores the transmitted information in the memory means with alarge capacity, and reads the information at the desired time for use.

Not all the transmission for transmission requests is real timetransmission, therefore, the number of immediate real time transmissionsis not so many, the reduced real time transmission allows thetransmission facility scale to be small. The centralization of thetraffic in prime time zone is prevented and the transmission capacitycan be used efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for describing an example of transmission frequencyband assignment in a two-way information transmission system.

FIG. 2 is a diagram for illustrating the use of going-down informationtransmission channels in the conventional video on-demand system.

FIG. 3 is a diagram for illustrating an example of a network structureof one embodiment of the two-way information transmission system inaccordance with the present invention.

FIG. 4 is a diagram for illustrating an example of a cable televisionstation structure as an information transmission center in oneembodiment of the two-way information transmission system in accordancewith the present invention.

FIG. 5 is a block diagram for illustrating a partial structure of thecable television station facility shown in FIG. 4.

FIG. 6 is a block diagram for illustrating an interchanging equipment inone embodiment of the two-way information transmission system inaccordance with the present invention.

FIG. 7 is a block diagram for illustrating an interchanging equipment inone embodiment of the two-way information transmission system inaccordance with the present invention.

FIG. 8 is a block diagram for illustrating a structural example of asubscriber terminal in one embodiment of the two-way informationtransmission system in accordance with the present invention.

FIG. 9 is a block diagram for illustrating a partial structure of thesubscriber terminal shown in FIG. 8.

FIG. 10 is a functional block diagram of a selected portion forillustrating one embodiment of the two-way information transmissionsystem in accordance with the present invention.

FIG. 11 is a diagram for illustrating the use of the going-downtransmission channels in one embodiment of the two-way informationtransmission system in accordance with the present invention.

FIG. 12 is a flow chart for describing an example of demand transmissionprocessing from a subscriber terminal in one embodiment of the two-wayinformation transmission system in accordance with the presentinvention.

FIG. 13 is a flow chart for describing an example of demand receivingprocessing in a cable television station in one embodiment of thetwo-way information transmission system in accordance with the presentinvention.

FIG. 14 is a flow chart for describing an example of receivingprocessing of going-down digital transmission data at a subscriberterminal in one embodiment of the two-way information transmissionsystem in accordance with the present invention.

FIG. 15 is a diagram for describing an example of the network structurein another embodiment of the two-way information transmission system inaccordance with the present invention.

FIG. 16 is a diagram for describing an example of transmission frequencyband assignment in another embodiment of the two-way informationtransmission system in accordance with the present invention.

FIG. 17 is a block diagram for illustrating a structural example of acable television station in another embodiment of the two-wayinformation transmission system in accordance with the presentinvention.

FIG. 18 is a block diagram for illustrating structural example of asubscriber terminal in another embodiment of the two-way informationtransmission system in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the two-way information transmission system in accordancewith the present invention will be described in detail referring to thedrawings for the example of video on-demand system. The direction from asubscriber to a cable television station is referred to as going-up, andthe inverse direction is referred to as going-down in the descriptionhereinafter.

FIG. 3 shows the outline of a network structure used for realizing avideo on-demand of an embodiment of the two-way information transmissionsystem. This example has the same structure as that of the two-way cabletelevision system described in the chapter of related art.

The cable television station HE called head end provides analogtelevision broadcast programs always during the broadcasting time zoneand also video programs in response to the demand from subscribers andother programs.

The cable television station HE can cover, for example, 8000 subscribersas described herein above, 8000 subscribers are divided into 16 sectionsand each section covers 500 subscribers MS. One interchange equipment IMcalled as optical fiber node (referred to as optical fiber node IMhereinafter) is installed for each section. An optical fiber node IMperforms mutual conversion between optical signal and electric signal.

In the case of this embodiment, an optical fiber cable FB connectsbetween each section and the television station HE in order to transmita signal without degrading in quality across a long distance. In eachsection, one coaxial cable CB is connected to an optical fiber node IM,and each subscriber MS is connected to the coaxial cable through acoaxial confluent distributor MPX. At most 500 subscribers MS areconnectable to one coaxial cable CB as described hereinbefore.

The cable television station HE has information sources including videoserver, and is connected to an optical fiber trunk SHW in order to fetchdigital information from the optical fiber trunk SHW and provide it tothe subscribers in addition to digital data from the digital informationsource of the cable television station HE itself. Further, a parabolaantenna AT is provided for receiving satellite broadcast, and receivedtelevision broadcast is supplied to respective subscribers as analogtelevision broadcast.

FIG. 4 shows an example of facility components of the cable televisionstation HE, and in this example, the facility comprises theabove-mentioned analog television broadcasting facility not shown inFIG. 4, for example video server 21 and tape information library system22 as a digital information source equipment, high speed ATM(non-synchronous transfer mode) exchanger 23, HE controller 24 forcontrolling the whole system of the cable television station HE, and 16node controllers 25a to 25p provided between 16 respective optical fibercables FB and ATM exchangers.

In this example, the video server 21 obtains, for example, 400 streamsas a bit stream of simultaneous transmission video signal. The codingrate of each bit stream data is, for example, 4 Mbits/sec, and, forexample, MPEG is used as a data compression system. In this case, twovideo servers may be provided as the video server 21 if, for example,simultaneous transmission stream quantity is 200 streams. Data VA ofeach video stream from the video server 21 is supplied to ATM exchanger23.

The tape information library system 22 is provided with a multi-shelfcontainer rack 22L in which many video tapes are placed on respectivelyspecified positions, a plurality of video tape players VRT1 to VTRn, anda retrieving transferring mechanism (not shown in the figure) which issuccessively operated for retrieving in the horizontal and verticaldirection to find out the position of a requested video tape in thecontainer rack 22L, for fetching the video tape, setting the video tapeinto any one of video tape players VTR1 to VTRn to playback the videotape, such tape information library system 22 is so-called as cartmachine. In this example, 160 video tape players are deployed.Therefore, the number of bit streams of the simultaneous transmissionvideo signal is 160.

Data VB of the digital video data stream of respective video tapeplayers VTR1 to VTRn has a transmission rate of, for example, 45Mbits/sec. The data VB is supplied to the ATM exchanger.

The tape information library system 22 provides programs more and easierthan the video server 21.

The HE controller 24 controls the whole cable television station HEincluding the control of the video server 21, control of the tapeinformation library system 22, and control of the ATM exchanger 23,generates a going-down control data DM to be transmitted to a subscriberand supplies it to the ATM exchanger 23 in response to an operationinput from an operator to the HE controller 24 and a going-up controldata UM (data such as a demand signal of the video on-demand) from asubscriber terminal supplied through the ATM exchanger 23.

Also digital data VC obtained from the optical fiber trunk SHW issupplied to the ATM exchanger 23.

The ATM exchanger 23 exchanges the above-mentioned digital data VA, VB,and VC, and going-down control data DM and divides or gathers them togenerate information necessary for respective transmission sections. TheATM exchanger 23 also transfers a going-up control data UM from asubscriber terminal to the HE controller 24.

Respective 16 node controllers 25a to 25p receive the analog televisionbroadcast signal AV and going-down information from the ATM exchanger23, and converts them to a signal having the frequency band previouslyassigned and converts an electric signal to light signal, and send it tothe optical fiber FB as described in FIG. 1. The respective 16 nodecontrollers 25a to 25p convert a going-up control data UM from a lightsignal to electric signal, and transfer it to the ATM exchanger 23.

Every node controllers 25a to 25p have the same structure. FIG. 5 is ablock diagram for illustrating the structure of one node controller outof the node controllers 25a to 25p. The optical fiber FB comprises threeoptical fibers fb1, fb2, and fb3.

The analog television information AV is supplied to a band pass filter102 through an input terminal 101, and converted to information having afrequency band of 50 MHz to 450 MHz, and supplied to theelectric-to-light converter 103.

The analog television information Av is supplied to the band pass filter102, converted to an information having a frequency of 50 MHz to 450MHz, and supplied to the electric-to-light converter 103. Theelectric-to-light converter 103 converts it to a light signal and sendsit to the optical fiber fb1.

In this example, as shown in the above-mentioned FIG. 1, 15 channels areallocated for the going-down digital transmission data of 45 M bits/secper one channel. Therefore, the node controller has 15 digitaltransmission data input terminals 104₁ to 104₁₅. The ATM exchanger 23switches directly the digital data such as video stream from the tapeinformation library system 22 to any one of 15 input terminals 104₁, to104₁₅ of a node controller corresponding to the section of the addresseesubscriber.

The ATM exchanger 23 switches a digital data of 4 M bits/sec bit streamfrom the video server 21 in a manner that at most 10 streams aremultiplexed and allocated to one channel.

Respective 45 M bits/sec digital data transmitted through the inputterminals 1041 to 10415 are supplied to hexternal QAM (QuadratureAmplitude Modulation) modulation circuits 105₁, to 105₁₅ respectivelyand modulated. The output data from the hexternal QAM modulationcircuits 105₁, to 105₁₅ are converted by the frequency conversioncircuits 106₁, to 106₁₅ respectively to signals of 15 channels which aresignals of 15 frequency bands with no superposing each other in thefrequency band ranging from 500 MHz to 708 MHz as shown in FIG. 1. Theoutput data from the frequency conversion circuits 106₁ to 106₁₅ aresupplied to the adding circuit 107 and the frequency of the data isconverted.

A node controller has an input terminal 110 for receiving 1.5 M bits/secgoing-down control data DM of one channel. The control data DM whichpassed through the input terminal 110 is supplied to QPSK (QuadraturePhase Shift Keying) modulation circuit 112 through the multiplexingcircuit 111, and subjected to QPSK modulation, and then supplied to afrequency conversion circuit 113 and converted to a signal of thegoing-down control channel near 500 MHz shown in FIG. 1. Subsequently,the signal is supplied to the adding circuit 107 and subjected tofrequency multiplexing.

The frequency multiplexed data from the adding circuit 107 is suppliedto the band pass filter 108 and subjected to band restriction to asignal in a frequency band ranging from 500 MHz to 708 MHz, and suppliedto the electric-to-light converter 109. The electric-to-light converter109 converts it to a light signal, and sends it to the optical fiber fb2as a digital transmission data.

The optical fiber fb3 is used for the going-up control channel, agoing-up control signal such as a demand of a subscriber which is QPSKmodulated and includes 45 channels by frequency multiplexing is suppliedto a light-to-electric converter 121 through the optical fiber fb3, andthe signal is converted from a light signal to an electric signal. Theoutput signal from the light to-electric converter 121 is supplied to aband pass filter 122 and subjected to the band restriction, and thenonly the going-up control data having a frequency band ranging from 900MHz to 972 MHz is fetched.

The control data from the band pass filter is supplied to 45 frequencyconversion circuits 123₁ to 123₄₅ corresponding to frequency bands of 45channels and subjected to frequency conversion, the frequency converteddata are processed as modulation data for respective channels. Themodulation data for each channel from the frequency conversion circuits123₁ to 123₄₅ is demodulated in a QPSK demodulation circuit 124₁ to124₄₅ to a control data of 1.5 M bits/sec. The control data is subjectedto time slicing multiplexing in the multiplexing circuit 111, and it issent to the ATM exchanger 23 through an output terminal 125 as agoing-up control data UM.

Next, the structure of the optical fiber node IM is described. FIG. 6 isa block diagram of an example of an optical fiber node.

A light-to-electric converter 201 receives an analog television signalthrough the optical fiber fb1for the analog television broadcast lineand converts it to an electric signal, thereafter supplies it to a bandpass filter 202. The band pass filter 202 fetches only an analogtelevision signal in a frequency band ranging from 50 MHz to 450 MHzfrom the input signal, and supplies it to an adding circuit 203.

A light-to-electric converter 204 receives a going-down digitaltransmission data of 15 channels through the optical fiber fb2 andconverts it to an electric signal, and supplies it to a band pass filter205. The band pass filter 205 fetches only a digital transmission datain a frequency band ranging from 500 MHz to 708 MHz from the input data,and supplies it to the adding circuit 203.

The adding circuit 203 adds the analog television broadcast signal anddigital transmission data for frequency multiplexing, and supplies thefrequency multiplexed signal to a band pass filter 207 through anamplifier 206. The band pass filter 207 performs band restriction within50 MHz to 708 MHz frequency band on the input signal, and thereaftersends the frequency multiplexed signal to the coaxial cable CB.

A data sent from a subscriber terminal through the coaxial cable CB issupplied to a band pass filter 208. The band pass filter 208 performsband restriction within 900 MHz to 972 MHz on the input data and fetchesa going-up control data, and supplies it to an electric-to-lightconverter 210 through an amplifier 209. The electric-to-light converter210 converts the going-up control data to an light signal and sends itto the optical fiber fb3.

Next, a structural example of a coaxial confluent distributor MPX isdescribed referring to FIG. 7. In detail, a going-down line data fromthe coaxial cable CB of the optical fiber node IM side is supplied to aband pass filter 211. The band pass filter 211 performs band restrictionon the input signal within a band ranging from 50 MHz to 708 MHz, andsupplies it to a distributor 212.

The distributor 212 supplies the going-down line data to a subscriberterminal connected to the coaxial confluent distributor MPX. Also, thedistributor 212 supplies the going-down line data to a band pass filter214 through an amplifier 213. The band pass filter 214 performs bandrestriction on the going-down line data for down-stream subscriberswithin a frequency band ranging from 50 MHz to 708 MHz, and sends it tothe coaxial cable CB.

A data from the down-stream side coaxial cable CB is supplied to a bandpass filter 215. The band pass filter 215 performs band restriction onthe input data within a frequency band ranging from 900 MHz to 972 MHzto allow the going-up control data to pass, and supplies it to asynthesis circuit 216. The synthesis circuit 216 adds the going-upcontrol data from down-stream subscribers and the going-up control datafrom the subscriber connected to the coaxial confluent distributor MPX,and supplies the synthesized data to a band pass filter 218 through anamplifier 217. The band pass filter 218 performs band restriction on theinput data within a frequency band ranging from 900 MHz to 972 MHz andsends it to the up-stream coaxial cable CB.

The frequency band for control data of respective subscribers ispreviously assigned so as not to overlap each other in one section.

Next, a structural example of a subscriber terminal ms provided in asubscriber's house MS is described referring to FIG. 8 and FIG. 9.

In detail, a going-down channel data from the coaxial confluentdistributor MPX is fed to an input terminal 301. A going-up control datais sent from an output terminal 302 to the coaxial confluent distributorMPX. The coaxial input terminal 301 and coaxial output terminal 302 areconnected to a demodulation/modulation unit.

The demodulation/modulation unit 303 has the structure shown in FIG. 9.In detail, a going-down line data from the coaxial input terminal issupplied to a band pass filter 304. The band pass filter 304 extracts ananalog television broadcast signal in a frequency band ranging from 50MHz to 450 MHz and supplies it to a frequency conversion circuit 305.

The frequency conversion circuit 305, which corresponds to a mixercircuit of a tuner, converts a signal of the broadcast program(broadcast channel) selected by a user out of received analog televisionbroadcast signals to a signal having a frequency which can bedemodulated by a subsequent analog television demodulation circuit 306in response to a channel select control signal corresponding to achannel select operation of the user supplied from a terminal controller320 described hereinafter, and supplies it to an analog televisiondemodulation circuit 306. The demodulation circuit 306 supplies thedemodulated television signal to a television through a switch circuit315 and video output terminal 316 shown in FIG. 8.

Further, a going-down line data from the coaxial input terminal 301 issupplied to a band pass filter 307. The band pass filter 307 extracts agoing-down digital data having a frequency in the band ranging from 500MHz to 708 MHz and supplies it to a frequency conversion circuit 308 andfrequency conversion circuit 309.

The frequency conversion circuit 308 converts only the signal of thechannel to which a video program delivered in response to the demandfrom the demand subscriber terminal based on a channel select controlsignal from the terminal controller 320 to a prescribed frequency whichcan be demodulated. A digital transmission data such as a video programdata addressed to the demand subscriber terminal from the frequencyconversion circuit 308 is supplied to a hexternal QAM demodulationcircuit 310 and demodulated. The 45 M bits/sec digital data from thedemodulation circuit 310 is supplied to the de-multiplexing circuit 317.

The frequency conversion circuit 309 frequency-converts the frequency ofa control channel data assigned previously to the demand subscriberterminal to a frequency which can be demodulated based on a channelselect control signal from the terminal controller 320. The going-downcontrol data from the frequency conversion circuit 309 is supplied to aQPSK demodulation circuit 311 and demodulated. The 1.5 M bits/seccontrol data from the demodulation circuit 311 is supplied to thede-multiplexing circuit 317.

A QPSK modulation circuit 312 of the demodulation/modulation unit 303receives a going-up control data, which will be described hereinafter,through the de-multiplexing circuit 317, and modulates it, and suppliesit to a frequency conversion circuit 313. The frequency conversioncircuit 313 frequency-converts the frequency of the input signal to afrequency of the control channel assigned to the demand subscriberterminal in a frequency band ranging from 900 MHz to 972 MHz. Thegoing-up control data from the frequency conversion circuit 313 is sentto the coaxial cable CB through a band pass filter 314 for bandrestriction in 900 MHz to 972 MHz and through the output terminal 302.

The de-multiplexing circuit 317 extracts a 4 M bits/sec digitaltransmission data addressed to the demand subscriber terminal from a 45M bits/sec output data supplied from the hexternal QAM demodulationcircuit 310 based on the control signal from the terminal controller 320if the digital transmission data is a 4 M bits/sec immediate real timetransmission data, and supplies it to a digital television signaldecoding circuit 319 through a switch circuit 318.

The digital television signal decoding circuit 319 decodes the digitaldata and converts it to an analog television signal, and supplies theanalog television signal to a television through the switch circuit 315and video output terminal 316.

The de-multiplexing circuit 317 sends the digital transmission datawhich is to be transmitted to the demand subscriber terminal to thetemporary memory means 330 and stores it temporarily in the case thatthe digital transmission data is a delaying transmission data referringto a control data from the terminal controller 320. In this case, thedelaying transmission data may be 4 M bits/sec rate or 45 M bits/secrate as described hereinafter.

A semiconductor memory 331 which is a data memory device having a largecapacity (about 1 G bits) and high speed transmission rate, hard diskdevice 332 (about 10 G bits), or data streamer 333 (about 200 G bits) isused as the temporary memory means 330.

These temporary memory means 330 stores the digital transmission datafrom the multiplexing circuit 317 according to a memory command from theterminal controller 320, and reads a stored data according to the readcommand from the terminal controller and supplies the data to thedigital television signal decoding circuit 319 through the switchcircuit 318.

In this case, as described hereinafter, the terminal controller 320determines which memory means is to be selected among the plurality ofmemory means of the temporary memory means 330 as the memory for storingthe going-down digital data dependently on the random access potentialand transmission format (such as data transmission rate) of the digitaldata to be stored which are specified by the going-down control data ordetermined by the demand sent by the demand subscriber terminal.

For example, if the data transmission rate is 4 M bits/sec and the datahas a low random access potential such as usual video program, then thedata is stored in the data streamer device 333 which uses tapes as therecording medium, on the other hand, if the data has high random accesspotential such as stock market information, then the data is stored inthe hard disk device 332, and if the data is a transmission data with adata transmission rate of 45 M bits/sec, then the data is written in thesemiconductor memory 331 capable of high speed writing, as describedherein, the memory means in which a data is to be stored is controlledand selected.

The de-multiplexing circuit 317 supplies a going-down control data fromthe QPSK demodulation circuit 311 to the terminal controller 320 bycontrolling the terminal controller 320.

The terminal controller 320 analyzes the going-down control data fed tothe terminal controller 320 through the de-multiplexing circuit 317, andif the control data is addressed to the demand subscriber terminal, theterminal controller 320 generates various control signals as describedherein above based on the control data. For example, the terminalcontroller 320 acquires various information that when the video datademanded by the demand subscriber terminal will be transmitted by way ofwhat channel out of 15 going-down channels in what transmission format,from the received going-down control data, and prepares for receiving.The channel select control signal to the frequency conversion circuit308, the control signal for multiplexing to the multiplexing circuit317, and the select control signal for selecting a memory device in thetemporary memory device 330 which are described herein above aregenerated from this going-down control data.

Further, the terminal controller 320 receives an operational input by auser through a user interface 321 comprising a remote control device andkey operation board, generates a going-up control data, namely demandsignal of video on-demand, and supplies it to the de-multiplexingcircuit 317. The terminal controller 320 controls the whole subscriberterminal ms.

A going-up control data such as video program demand sent from theterminal controller 320 to the de-multiplexing circuit 317 is suppliedsuccessively to the QPSK modulation circuit 312 of thedemodulation/modulation unit 303, frequency conversion circuit 313, andband pass filter 314, modulated as described hereinbefore,frequency-converted to a signal of the control channel assigned to thedemand subscriber terminal, and sent to the cable television station HE.

The de-multiplexing circuit 317 is connected to CATV telephone terminal(not shown in the figure) through the terminal 341 and 342, subscriberscan communicate with operators of the cable television station HE.

The information transmission mechanism and transmission of a signal inthe two-way CATV system having the system structure as described aboveare described hereinafter.

Analog Television Broadcast

Analog television broadcast is transmitted from the cable televisionstation HE to subscriber terminals ms by way of one-way transmission asusual without demand from subscribers.

When a user wants to view an analog television broadcast from the cabletelevision station HE, the user operates channel select operation forselecting an analog television broadcast of the cable television stationHE through the user interface 321 of the subscriber terminal ms. Then,the terminal controller 320 of the subscriber terminal ms supplies achannel select signal corresponding to the channel select operation ofthe user to the frequency conversion circuit 305 of thedemodulation/modulation unit 303, and the switch circuit 315 is switchedto the mode for selecting an analog television signal from the analogtelevision demodulation circuit 306 of the demodulation/modulation unit303, and thereby an analog television signal is supplied from the videooutput terminal 316 to a television. Thus the subscriber can view ananalog television broadcast program selected by the user from the cabletelevision station.

Digital Information Transmission

FIG. 3 is a block diagram for describing mainly functions which areperformed at the HE controller 24 of the cable television station HE andthe terminal controller 320 of a subscriber terminal ms to transmitdigital information in the system of the above-mentioned embodiment inwhich the cable television station HE and subscriber terminals ms areconnected through the going-up and going-down lines comprising opticalfiber and coaxial cable.

As shown in FIG. 3, the cable television station HE provided as aninformation distribution transmission center is connected to a pluralityof subscriber terminals ms through the going-up line Cu which is theline for transmission toward the cable television station and thegoing-down line Cd.

The cable television station HE comprises functions of a digitalinformation source 1 comprising a video server 21 and tape informationlibrary system 22, going-down information signal generator 2 comprisingan ATM exchanger 23 and node controllers 25a to 25p, informationtransmission control means 3 for controlling a digital informationsource 1 and controlling a going-down information signal generator 2 tocontrol transmission of an going-down digital information, transmissionplanning means 4, and demand receiving analysis means 5. The informationtransmission control means 3, transmission planning means 4, andanalysis section of the demand receiving analysis means 5 are realizedas functions of the HE controller 24 (realized by soft ware).

Each subscriber terminal ms is provided with a demand transmission means11 for sending a demand (transmission request) to the going-up line Cu,temporary memory means 12 having a large capacity, transmission planreceiving analysis means 13 for receiving a going-down control dataaddressed to the demand subscriber terminal and analyzing thetransmission plan information, and transmission information receivingcontrol means for receiving and demodulating a digital transmission dataaddressed to the demand subscriber terminal from the going-down line Cdand then supplying the modulated data to a monitor television not shownin the figure if the data is required to be regenerated in real time, orstoring the received transmission information addressed to the demandsubscriber terminal in the temporary memory means 12.

The demand transmission means 11 receives a demand of a user through theuser interface such as a remote controller or key board, generates adistribution transmission signal, and sends it to the going-up line Cu.

A demand signal includes a user ID which is an identification code ofeach subscriber, transmission program specifying information (programidentifying data) for specifying a video program requested fordistribution, request time information which is a information relatingto urgency of the requested information such as the time when theprogram is desired to be transmitted or the time when the subscriberwants to view, and transmission format specifying information forspecifying which format of 4 M bits/sec digital information or 45 Mbits/sec digital information is desired.

In this case, the information of the time may be used as it is as therequest time information, however in this embodiment, several classesare defined depending on the urgency of a request, and the request timeinformation specifies a class. In detail, 1 if a user wants to view theprogram immediately, then the program is demanded as A-class urgency, 2if a user wants to view later, then the program is demanded as B-classurgency, and 3 if a user wants to view within a half or one day, thenthe program is demanded as C-class urgency.

In this embodiment, the going-down digital information transmissionchannel includes digital television broadcast channel, a program of thedigital television broadcast can be viewed without intentional demand bya subscriber. The class of this digital television broadcast channel isreferred to as D-class hereinafter.

In this embodiment, in the 45 MHz×15 channel transmission band for thegoing-down digital transmission data, the transmission capacity isallocated dynamically to the demand urgency classes dependently on theactual traffic condition of respective time zones in a day in order touse efficiently the transmission capacity.

For example, in prime time zone, the capacity is allocated as describedhereinunder.

Transmission to A-class demand: 45 M bits/sec×5 channels

Transmission to B-class demand: 45 M bits/sec×8 channels

Transmission to C-class demand: No allocation

Transmission to D-class: 45 M bits/sec×2 channels

In midnight time zone when a few demands are generated, the capacity isallocated as described herein under.

Transmission to A-class demand: 45 M bits/sec×2 channels

Transmission to B-class demand: 45 M bits/sec×2 channels

Transmission to C-class demand: 45 M bits/sec×10 channels

Transmission to D-class: 45 M bits/sec×1 channel

It is considered that many demands for video programs are requested inprime time, no program is transmitted to C-class demands and more numberof channels is allocated for transmission to A-class and B-class demandsin order to transmit programs with a waiting time as short as possible.

Two channels are allocated to D-class transmission in order to providemany digital broadcast programs in prime time.

On the other hand, it is considered that a few demands for digitaltelevision broadcast programs is requested in the midnight time zone andthe number of broadcast programs may be not many, the number oftransmission channels for digital television broadcast is reduced by onechannel comparing with the number in prime time zone. It is consideredthat a fewer demands for video programs is requested in the midnighttime zone than in prime time zone, then the number of channels fortransmission to A-class and B-class demands is reduced, and moretransmission capacity and more channel are allocated to C-class demandsso that C-class demands which have been accepted previously aretransmitted.

An example of the allocation of transmission capacity for the going-downdigital transmission data allocated as described herein above is shownin FIG. 11. In FIG. 11, the abscissa represents the time, and the axisof ordinate represents the allocation of 15 channel capacity for thedigital transmission data.

An arrow ↑ represents a time point of generation of a distributiontransmission request command, and a section enclosed by a rectanglerepresents a program. "For broadcast" represents the transmissioncapacity for digital television broadcast, "real time V. 0. D."represents the transmission capacity for real time transmission ofA-class demands, "little delay V. 0. D" represents the transmissioncapacity for digital information transmission of B-class demands, and"much delay V. 0. D" represents the transmission capacity for digitalinformation transmission of C-class demands like the above-mentionedFIG. 2.

As shown in FIG. 11, no transmission capacity is allocated fortransmission of C-class demands in primetime. The allocated channels"real time V. 0. D" transmits in real time in response to a demand, andthe allocated channel "little delay V. 0. D" transmit with a littledelay from a demand with looking for a free channel. The transmissiontime of one program can be shorter than the transmission time by way ofthe allocated channel to "real time V. 0. D" because of 45 M bits/sectransmission in this case.

In the midnight time zone, more channels are allocated to "much delay V.0. D", and many programs are transmitted to the previously acceptedC-class commands which allows much delay. Accordingly, the midnight timezone when usually a little demand is generated is used efficiently, andthe transmission is performed efficiently.

Generation and transmission of distribution transmission request signal!

FIG. 12 is a flow chart of routine for generation and transmission ofdemand signals of video on-demand at a subscriber terminal.

Upon receiving a command input for sending a distribution transmissionrequest form a user through the user interface in the subscriberterminal ms, the processing routine shown in FIG. 12 starts. In detail,a operational input of a user is received in the step S1, what class isspecified as request time information is judged in the next step S2. Ifthe request time information is A-class, then the process proceeds tothe step S3 and A-class demand signal is generated, then the demandsignal is sent to the going-up line Cu in the step S6.

If the request time information is B-class or C-class, the processproceeds to the step S4, the specification of transmission format isjudged to be transmission rate of the transmission data of 4 M bits/secor 45 M bits/sec, and the specification of random access is judged.Then, the process proceeds to the next step S5, a demand signalincluding the judged format, random access, and urgent class isgenerated, and the demand signal is sent to the going-up line Cu in thestep S6.

The distribution transmission request demand signal includes a user IDfor identifying the subscriber terminal and a program identifying datafor identifying a desired video program as described hereinbefore.

Receiving processing of distribution transmission request demand!

FIG. 13 is a flow chart of processing routine for receiving a demandsignal from a subscriber terminal in the HE controller 24 of the cabletelevision station HE.

Upon receiving the demand signal sent from a subscriber terminal throughthe going-up line Cu, the transmission request receiving analysis means5 of the cable television station HE transfers the request timeinformation included in the demand signal to the transmission planningmeans 4, and transfers the user ID and program identifying data to theinformation transmission control means 3. (step S11).

The transmission planning means 4 analyzes the request time information,and judges which demand class of A-class, B-class, or C-class isincluded in the request time information included in the demand signal(the step S12). If the request time information is A-class whichrequests real time transmission, then the transmission planning means 4looks for a free going-down line transmission channel assigned to "forreal time V. 0. D" shown in FIG. 11, and if the transmission planningmeans 4 finds a free channel, then the free channel is decided to be areal time transmission channel (the step S13).

Upon receiving this decision, the information transmission control means3 informs of the real time transmission channel to the subscriber whosent the demand (the step S14), and extracts the video program specifiedby the program identifying data from the digital source 1, and performsthe real time transmission (the step S15).

When, the digital transmission data is fetched from the video server 21and transmitted by way of the channel of the above-mentioned "for realtime V. 0. D".

If the request time information judged in the step S12 is B-class and isthe transmission request which allows a little delay, the transmissionplanning means 4 looks for a free channel from the going-down channel"for little delay V. 0. D" in FIG. 11 for B-class, and decides atransmission time so as to transmit by way of the free channel (the stepS16).

The transmission planning means 4 informs of the free channel to be usedfor the transmission, transmission time, and above-mentioned analysisresult to the information transmission control means 3. Further, thetransmission planning means analyzes the transmission format informationincluded in the demand signal and random access information, and informsof the analysis result to the information transmission control means 3.

The information transmission control means 3 transmits previously thefree channel, transmission time (starting time and ending time),transmission format (4 M bits/sec transmission rate or 45 M bits/sectransmission rate), and random access information to the subscriber whosent the demand and is specified by the user ID as the going-downinformation having the user ID header information (the step S18), whenthe time comes to the transmission time (the step S19), the informationtransmission control means 3 extracts the specified video program basedon the program identifying data included in the transmission requestdemand and transmission format from the video server 21 in the case ofthe transmission rate of 4 M bits/sec or from the tape informationlibrary system 22 in the case of the transmission rate of 45 M bits/sec,and transmits it (the step S20).

If the request time information is determined to be C-class in the stepS12, that is, the transmission request allows much delay of a half dayto one day, the transmission planning means 4 finds out a free channelfrom the transmission plan of the going-down line channels (("for muchdelay V. 0. D) shown in FIG. 11) assigned to the midnight time zone, anddecides a transmission time so as to transmit by way of the free channel(the step S17).

Then, the transmission planning means 4 informs the free channel to beused for the transmission, transmission time, and above-mentionedanalysis result to the information transmission control means 3.Further, the transmission planning means 4 analyzes the transmissionformat information included in the demand signal and random accessinformation, and gives the analysis result to the informationtransmission control means 3.

The information transmission control means 3 transmits previously thefree channel, transmission time (starting time and ending time),transmission format (4 M bits/sec transmission rate or 45 M bits/sectransmission rate), and random access information to the subscriber whosent the demand and is specified by the user ID as the going-downcontrol data having the user ID header information (the step S18), andwhen the time comes to the transmission time (the step S19), theinformation transmission control means 3 extracts the specified videoprogram based on the program identifying data included in thetransmission request demand and transmission format from the videoserver 21 in the case of the transmission rate of 4 M bits/sec or fromthe tape information library system 22 in the case o f the transmissionrate of 45 M bits/sec, and transmits it (the step S20).

Receiving processing of a control data and transmission data in asubscriber terminal!

FIG. 14 is a flow chart of a processing routine performed when theterminal controller 320 of a subscriber terminal receives a going-downcontrol data and transmission digital data.

The subscriber terminal receives a control data of the transmission planaddressed to the demand subscriber terminal referring to the user ID inthe going-down control data from the going-down line Cd (the step S21),analyzes it (the step S22), and judges whether it requires the immediatereal time transmission referring to the analysis result (the step 523).The judgment may be based on, for example, no inclusion of transmissiontime data in the going-down control data. Alternately, a classinformation or flag which indicates whether it requires the real timetransmission or does not is included in the going-down control data, andthe judgment may be performed based on the class information or flag.

If the judgment result based on the analysis shows the real timetransmission, the terminal controller 320 acquires the information ofthe transmission channel, and supplies a select signal for convertingthe going-down digital transmission data of the transmission channel toa data having a frequency band which can be demodulated to the frequencyconversion circuit 308, switches the switch circuit 318 so as to select4 M bits/sec data from the de-multiplexing circuit 317, and switches theswitch circuit 315 so as to select the television signal from thedigital television decoding circuit 319 to supply it to a televisionthrough the output terminal 316 (the step S24).

If the judgment result in the step S23 does not show an immediate realtime transmission, then the terminal controller 320 recognizes thetransmission time, transmission channel, transmission format, and randomaccess information based on the analysis result of the above-mentionedgoing-down control data, and prepares for receiving (the step S25). Theterminal controller 320 waits for the transmission time of thetransmission information (the step S26), and when the time comes to thetransmission time, the terminal controller 320 supplies a select signalfor converting the going-down digital transmission data of thetransmission channel to a data having a frequency band which can bedemodulated to the frequency conversion circuit 308, and starts toreceive the digital transmission data according to the transmissionformat (the step S27).

Any one medium which is to be used for storing the transmissioninformation is selected previously from the semiconductor memory, harddisk device, data streamer, and digital VTR in the temporary memorydevice 320 according to the transmission format included in thegoing-down control data and random access information (the step S28),and the received transmission information is stored in the selectedtemporary memory device (the step S29).

In this case, if the transmission format specifies high speedtransmission and the semiconductor memory is selected as the temporarymemory means, the transmission information is transmitted with the highspeed transmission rate of 45 M bits/sec, and the transmission data isstored in the semiconductor memory 331 which serves as the temporarymemory means as it is high speed transmission rate.

For example, if the transmission rate of a compressed digital data is1.5 M bits/sec and a program is a two-hour program, the programcompressed to 45 M bits/sec rate is transmitted, then the transmissionrequires only about 4 minutes, and alternately if the transmission rateis 4 M bits/sec, the transmission of a two-hour program requires onlyabout 11 minutes.

In the case that the transmission date rate is 4 M bits/sec due to thetransmission format, the selection of a temporary memory mans depends onrandom access, and the hard disk device is selected for high randomaccess and the data streamer device 333 is selected for low randomaccess as the temporary memory means.

High fee may be applied to the request for low rate format transmissionin real time, on the other hand, low fee may be applied to the requestfor high speed rate because the transmission time is short.

As described herein above, the receiving processing of the transmissioninformation is performed in a subscriber terminal. The television signalreceived in real time transmission is supplied to a television withoutstoring in the temporary memory device. Therefore, a user can view theprogram with a slight delay from the demanding.

On the other hand, the video data stored in the temporary memory device330 is regenerated at the arbitrary time and provided to the subscriberin response to a regeneration request from the subscriber through theuser interface 321. In detail, the subscriber inputs a regenerationrequest of the program which was transmitted with a delay through theuser interface 321, the terminal controller 320 receives theregeneration request, and sends a regeneration command to the temporarymemory device in which the video program is stored.

Upon receiving the regeneration command, the temporary memory devicereads the corresponding digital video data of the program, and suppliesit to the digital television decoding circuit 319 through the switchcircuit 318. In this case, the rate of the read digital data is 4 Mbits/sec. The video signal from the decoding circuit 319 is supplied toa television through the output terminal 316, and provided to the user.

For the case that a plurality of video programs is registered in thetemporary memory device due to a plurality of demands, the terminalcontroller 320 of a subscriber terminal ms is provided with a functionto display the menu of accumulated video programs, the user can selectand view any program from the menu.

In this embodiment, a program stored in the temporary memory device 330is once regenerated in response to a regeneration request by the user,then the program is erased from the corresponding temporary memorydevice in response to an erasing command from the terminal controller320 to prevent the program information from being copied illegally.

In the first embodiment described herein above, a user can demand notonly the immediate real time transmission but also the delayedtransmission, therefore, a user who wants to view the program in primetime zone can demand for the program to be transmitted during themidnight time zone and the program is stored in the temporary memorydevice, and the user can view the demanded program at the desired time.

The above-mentioned demand-delayed view system favors the demand forimmediate real time transmission in prime time to decrease. Many typesof demand are available dependent on the urgency classes, therefore, forexample, it is possible to apply the lower fee to the demand allowableof delayed transmission than that to the demand for immediate real timetransmission, such fee system favors the demand in prime time todecrease.

Such suppressed generation of the immediate real time transmission inprime time allows the cable television station to be provided with asmaller scale facility in comparison with the conventional cabletelevision station which transmits programs only in real time.

Transmission capacity of going-down digital transmission data isallocated to an independent plurality of transmission channels dependingon the information relating to the urgent class in the demand and manychannels are allocated to the immediate real time transmission in primetime, on the other hand, many channels are allocated to the delayedtransmission in midnight, such change of allocation depending on thetime zone allows the transmission capacity to be used efficiently.

In the above-mentioned embodiment, high speed transmission is possiblefor delayed transmission in comparison with real time transmission, andthe time required for transmission of one program is shortened incomparison with the conventional method, in this aspect also, thetransmission capacity is used efficiently.

In the above-mentioned first embodiment, allocation of the number oftransmission channels depending on the information relating to theurgency class of the demand is changed in the time zone in a day, butthe allocation may be changed dependently on days in a week, or may bechanged in combination of time zone and week.

In the above-mentioned embodiment, the allocation of transmissionchannels depending on the information relating to the urgency class ofthe demand is changed within only the transmission capacity of thegoing-down digital information data, but, because the audience rate ofanalog television broadcast decreases, the transmission band of analogtelevision broadcast is reduced and the reduced transmission band isused as the transmission band of digital information data.

In this case, a program table including channel assignment differentbetween prime time and midnight is prepared for analog televisionbroadcast, and this program table is transmitted to subscriberspreviously to inform the change of program channel depending on the timezone.

A plurality of data compression systems of digital transmission data isprovided in the cable television station, for example, depending onrequested degree of resolution, and any one of data compression systemsmay be selected by way of the demand from a subscriber terminal. In thiscase, a plurality of decoders are provided in a subscriber terminaldepending on the above-mentioned plurality of data compression systems,the information including compression system information in thegoing-down control data from the television station is sent to thesubscriber terminal, and the decoder is switched dependently on thecompression system information.

In the above-mentioned embodiment, B-class demand is stored necessarilyin the temporary memory means, but because it is possible to display thetransmission time sent from the station on a display of a subscriberterminal and to inform it to a user, a mode for specifying real timetransmission regeneration for B-class demand without storing in thetemporary memory means may be provided.

Further in the above-mentioned embodiment, the temporary memory means isselected based on the transmission format and random access relatinginformation in the going-down control data in a subscriber terminal, butalternately a demand signal sent from a subscriber terminal is stored inthe subscriber terminal, and the temporary memory means may be selectedfor the transmitted transmission data depending on the stored demandsignal. In this case, an identification data ID for identifying thedemand signal may be added in the demand signal to judge the demand. Inthis case, the information relating to transmission format and randomaccess is not necessarily included in the going-down control data.

Second embodiment

The second embodiment shows an example in which an existing CATV cablenetwork is used. In a conventional CATV cable network, a cabletelevision station is connected to a plurality of subscriber terminalsby way of coaxial cable, and provides mainly analog television broadcastto each subscriber terminal by way of coaxial cable.

In the second embodiment, a facility for transmission of digital datasuch as video data is added to a cable television station without changeof the conventional transmission line facility using coaxial cable, anda receiving unit for receiving digital data provided with a largecapacity temporary memory device is added to a subscriber terminal. Thepublic phone network is used as the going-up line for transmission ofdigital data demand.

FIG. 15 shows the whole network structure of the embodiment. In a cabletelevision station 40, an analog television broadcast signal Va from theabove-mentioned analog television broadcast facility 401 and digitaldata Vb such as digital video data from the digital transmission datatransmission facility 402 are synthesized to generate a frequencymultiplexed signal, and sent to the coaxial cable CB through anamplifier 404.

A plurality of telephone lines L1 to Ln is connected to the public phonenetwork PSTN, and a station side controller 405 for receiving demandsfrom subscribers through the telephone lines L1 to Ln and for sendingvideo programs corresponding to the demand from the digital datatransmission facility 402.

Also in this embodiment, the station side controller 405 generates agoing-down control data Vc including a user ID for specifying theaddressed subscriber terminal which receives the digital data, programID, transmission channel, and transmission time information in order tosend the digital data to the subscriber terminal which transmitted thedemand, supplies it to a synthesizer 403 to frequency-multiplex theinformation for transmission of the going-down control data Vc, andsends it to a subscriber terminal.

FIG. 16 shows the frequency assignment of frequency multiplexed signalfor transmitting in the coaxial cable CB, 50 MHz to 450 MHz frequencyband is used for analog television broadcast signals as it is usedconventionally. The frequency band around 500 MHz is used for thegoing-down control data having a transmission rate of 1.5 M bits/sec asit is used in the above-mentioned embodiment. Two frequency bands inhigher frequency are used for transmission of the going-down digitaldata having a transmission rate of 45 M bits/sec. In other words, twochannels are assigned to digital data.

Subscriber terminals 50 are connected to the coaxial cable CB throughcoaxial confluent distributors 60 as it is so connected in the sectionalnetwork in the above-mentioned embodiment. The coaxial confluentdistributor 60 comprises an input buffer amplifier 61 for receivinginformation from the coaxial cable CB connected to the coaxial confluentdistributor connected in front, a distributor 62 for identifying thesignal between a signal to be distributed to the subscriber terminalconnected to the coaxial confluent distributor and a signal to bedistributed to subscriber terminals in the down stream, and an outputbuffer amplifier 63 for supplying output signal to subscriber terminalsin the down stream.

A subscriber terminal 50 is connected to the public phone network PSTNthrough a telephone line Lms as shown in FIG. 15. A telephone 70 isconnected to the telephone line Lms through the subscriber terminal 50,and a television 80 is connected to the subscriber terminal 50.

The cable television station 40 has in detail, for example, a structureshown in a block diagram of FIG. 17. In detail, an analog televisionbroadcast signal Va is subjected to band restriction to generate asignal of the band for the above-mentioned analog television broadcastthrough a band pass filter 411, and thereafter is sent to a synthesiscircuit 403.

The digital transmission data transmission facility 402 is provided witha tape information library system 412. The tape information librarysystem 412 comprises a tape container rack 412L, a plurality of playersVTRa to VTRd, a transferring mechanism (not shown in the figure) fortaking out a desired cassette tape from the tape container rack and forcharging it to any one of the players VRTa to VTRd as it is sostructured in the above-mentioned embodiment, but in this secondembodiment, two players VTR are provided to each channel, that is, totalfour players VTRa, VTRb, VRTc, and VTRd are provided, the facility issimplified in comparison with the tape information library system of theabove-mentioned cable television station HE having the digital facility.

The station side controller 405 controls the selection of a channel outof the two channels and decides the selection of a player out of the twoplayers by switching and controlling switch circuits 413 and 414.

Digital data from respective switches 413 and 414 is modulated inhexternal QAM modulation circuits 415 and 416 as it is so modulated inthe above-mentioned embodiment, subsequently supplied to the frequencyconversion circuits 417 and 418, and frequency-converted to a signal ofthe band for each channel shown in FIG. 16. The output signal of thefrequency conversion circuits 417 and 418 is supplied to the synthesiscircuit 403.

A going-down control data Vc from the station side controller 405 issupplied to a QPSK modulation circuit 419 and modulated, thenfrequency-converted to a signal of the band for control data shown inFIG. 16. The output signal from the frequency conversion circuit 420 issupplied to the synthesis circuit 403.

A going-up demand data sent from a subscriber terminal through thetelephone lines L1 to Ln is taken in the station side controller 405through modulators 421 to 42n. The going-down control data Vc isgenerated based on the going-up demand data. The demand data includes auser ID for identifying the subscriber terminal, data for identifyingthe requested program, and request time information describedhereinafter.

Next, a subscriber terminal has a structure, for example, shown indetail in a block diagram of FIG. 18.

The going-down signal from the coaxial confluent distributor 60 issupplied to band pass filters 502 and 503 through a input terminal 501.The band pass filter 502 has a pass band of the analog televisionbroadcast signal frequency band shown in FIG. 16, the analog televisionsignal obtained from the band pass filter 502 is supplied to a frequencyconversion circuit 504.

The channel selection control signal corresponding to the channelselection operation through the user interface 530 from the terminalcontroller 520 is supplied to the frequency conversion circuit 504, andthe analog broadcast program channel signal selected by a user isconverted by the frequency conversion circuit 504 to a signal of afrequency which can be demodulated by the subsequent analog televisiondemodulation circuit 505. The output signal from the frequencyconversion circuit 504 is supplied to the analog television demodulationcircuit 505, and the television signal of the above-mentioned selectedanalog television broadcast program channel is demodulated. Thedemodulated television signal is supplied to an output terminal 507through a switch circuit 506.

A television 70 is connected to the output terminal 507. A userinterface 530 comprises a remote controller and key board device as itso comprises in the above-mentioned embodiment.

The going-down control data and going-down digital information data areobtained from the band pass filter 503. The going-down control data isconverted by a frequency conversion circuit 512 to a signal of a bandwhich can be demodulated by the subsequent QPSK demodulation circuit513, then supplied to a QPSK demodulation circuit 513 and demodulated.The demodulated control data is supplied to a de-multiplexing circuit514, and only the control data of the channel given to the demandsubscriber terminal by the control signal from the terminal controller520 is taken out, and supplied to the terminal controller 520.

The terminal controller 520 interprets the control data, judges whetherthe control data is addressed to the demand subscriber terminal based onthe user ID included in the control data, and if the control data isaddressed to the demand subscriber terminal, the terminal controller 520analyzes the control data and informed of the above-mentioned programID, transmission time, and transmission channel (which channel out ofthe digital data transmission channels).

The digital information data from the band pass filter 503 is suppliedto a frequency conversion circuit 508. In the frequency conversioncircuit 508, only the information data of the transmission channel foundby analyzing the above-mentioned control data is converted to a signalof a frequency which can be demodulated by a hexternal QAM demodulator504 based on the control signal from the terminal controller 520. Theoutput signal from the frequency conversion circuit 508 (¥3) is suppliedto the hexternal QAM demodulation circuit 509 and demodulated, thedemodulated signal is supplied to a data streamer device 510 andtemporarily stored.

The terminal controller 520 outputs a regeneration command including theprogram ID to the data streamer device 510 in response to theregeneration request input including the program ID through the userinterface 530 of the user. The data streamer device 510 reads andregenerates the digital information specified by the program ID out oftemporarily stored information in response to the regeneration command.

The read digital information is subjected to error correction decodeprocessing in a digital television signal decoding circuit 511,converted to an analog television signal, and supplied to the switchcircuit 506.

The switch circuit 506 is switched either to the analog demodulationcircuit side for analog television broadcast receiving channel selectionor to the digital television signal decoding circuit 511 side forviewing the temporarily stored program dependently on the switchingsignal from the terminal controller 520 in response to the user inputthrough the user interface 530, the user can view the respectiveprograms in the television connected to the output terminal 507.

The terminal controller 520 generates a demand signal as a going-up datain response to a demand input for a digital information program throughthe user interface 530. The demand signal includes the user ID, ID ofthe demanded program, and request time information of the urgency forthe demanded program as it so includes in the above-mentionedembodiment. If the same plurality of compression methods as used fordigital transmission of video signal transmitted from the cabletelevision station side is provided and a user can select thecompression method dependently on the demanded information and necessaryresolution, then the demand signal includes the transmission format suchas data compression ratio.

The demand signal from the subscriber terminal is modulated by amodulator 521, and sent out to the telephone line Lms connected to thepublic telephone network through NCU (network control unit) 522. Atelephone 70 is connected to NCU 522 through the telephone terminal 524,and the telephone 70 is used as it is used usually.

In the second embodiment, the cable television station 40 is acceptableof only transmission request for delay allowable demands correspondingto B-class and C-class demands in the above-mentioned first embodiment.More in detail, real time transmission and digital television broadcastare not involved, two-way information transmission is realized only withadding some additional facility to the existing cable television systemfacility.

In this embodiment, when a user inputs a demand to the subscriberterminal, the user selects a request time information which is eitherB-class demand allowable of little delay or C-class demand allowable ofa delay of from a half day to one day.

Upon receiving the demand from the user through the public telephonenetwork PSTN, the cable television station 40 plans a transmission planso as to transmit successively requested programs if the demand isB-class. In detail, if there is a free channel in the going-down digitalinformation data band, the cable television station 40 plans thetransmission plan so as to transmit the demanded program information tothe subscriber terminal by way of the free channel.

Upon completion of the transmission plan, the cable television station40 transmits previously a going-down information including the time whenthe requested program is to be transmitted, the channel to be used forthe transmission, and the going-down control data including transmissionformat information to the subscriber terminal which transmitted thedemand.

The subscriber terminal 50 acquires the control data addressed to thedemand subscriber terminal, and is informed of previously the time to betransmitted, channel to be used for the transmission, and transmissionformat, and prepares for receiving. Monitoring the time for finding thetransmission time, the subscriber terminal 50 receives the digitalinformation data transmitted with a address to the demand subscriberterminal 50 through the above-mentioned band pass filter 503, frequencyconversion circuit 508, and hexternal QAM demodulation circuit 509, andstores the received digital information data in the data streamer device510.

When the user input at an arbitrary time a regeneration request for theselected specified program out of temporarily stored programs throughthe user interface 530, the terminal controller 520 sends a regenerationcommand of the specified program to the data streamer device 510. Thedata streamer device 510 reads and regenerates the specified program inresponse to the regeneration command, and supplies the television signalto the television through the output terminal 507, and the user can viewthe program.

As described herein above, in the case of the second embodiment, thereal time transmission is not necessary, the introduction of a largescale system such as video server is not necessary, the video on-demandsystem is realized with a relatively small investment, the digitalinformation data can be transmitted with a delay efficiently during thetime zone such as midnight when traffic is infrequent, thus thetransmission band can be used efficiently.

A demand signal is sent to the television station through the publictelephone network, therefore it is unnecessary to provide extratransmission line for going-up data, thus extra investment for thispurpose is not necessary.

The application of this invention to the video on-demand system isdescribed hereinbefore, however, the present invention can be applied tonot only video system but also other every two-way informationtransmission systems which transmit various information in response to ademand.

As described hereinbefore, according to the present invention, the videoon-demand system can be realized without introduction of large scalesystem such as video server and with relatively small investment. Thecentralization of traffic is mitigated, and the network resource is usedefficiently.

What is claimed is:
 1. A two-way information transmission system provided with an information distribution transmission center and at least one subscriber terminal connected to said information distribution transmission center via an up-going line and a down-going line, said subscriber terminal sending an information distribution transmission request to said information distribution transmission center through said up-going line, and said information distribution transmission center transmitting requested information in response to said request through said down-going line, said two-way information transmission system comprising:an information distribution transmission center including:transmission planning means for planning a transmission plan to transmit requested information based on an information distribution transmission request from a subscriber terminal, transmission means for transmitting said requested information based on said transmission plan planned by said transmission planning means, a plurality of transmission channels allocated for use for a plurality of urgency levels, wherein a number of said plurality of transmission channels allocated for a high urgency level increases in accordance with an increase in a number of requests for information distribution transmission, and down-going control data sending means for sending down-going control data including information involving said transmission plan planned by said transmission planning means to said subscriber terminal which sent said information distribution transmission request, before said transmission means transmits said requested information; and a subscriber terminal including:distribution transmission request sending means for sending said information distribution transmission request including at least information for identifying said subscriber terminal making said request, information for identifying said requested information, and urgency information relating to an urgency level of said requested information, said urgency information including a real time transmission request, memory means, transmission plan receiving analysis means for receiving and analyzing said transmission plan based on said down-going control data from said information distribution transmission center, information acquisition means for acquiring said requested information transmitted from said information distribution transmission center based on said transmission plan and storing said requested information in said memory means, wherein when said urgency information is a real time transmission request said requested information transmitted from said information distribution transmission center is supplied without being stored in said memory means, and when said urgency information is other than said real time transmission request said requested information is stored in said memory means, said requested information having been acquired by said transmission plan receiving analysis means, and reading means for reading said information from said memory means.
 2. The two-way information transmission system as claimed in claim 1, whereinsaid urgency information included in said information distribution transmission request specifies any one of said plurality of urgency levels which have different respective delay times from said distribution transmission request to transmission of said requested information depending on said urgency level of said urgency information, and said transmission planning means determines a transmission time based on said urgency level included in said information distribution transmission request.
 3. The two-way information transmission system as claimed in claim 1, wherein said information distribution transmission center transmits in real time in response to said real time transmission request which requests immediate transmission, and transmits in a free channel of an available time zone when said urgency information allows for a time delay before transmission.
 4. The two-way information transmission system as claimed in claim 1, wherein said transmission means transmits said requested information after data compression, and selects a data compression method from a plurality of data compression methods according to a type of information to be transmitted.
 5. The two-way information transmission system as claimed in claim 4, whereinat least one of said plurality of data compression methods used by said transmission means transmits said requested information at a speed faster than a data transmission speed of information regenerated in real time in said subscriber terminal, and said memory means of said subscriber terminal stores said transmitted requested information at a high speed.
 6. The two-way information transmission system as claimed in claim 1, whereinsaid memory means comprises a plurality of recording devices disposed in parallel, said plurality of recording devices including tape type recording media, sheet type recording media, card type recording media, disk type recording media, and semiconductor memories, and said information acquisition means records said information in a recording device selected from said plurality of recording devices depending on a volume of said information to be stored and a degree of random access required.
 7. A method of two-way information transmission in which a subscriber terminal requests an information distribution transmission from an information distribution transmission center through an up-going line, and said information distribution transmission center transmits said requested information in a down-going line in response to said information distribution transmission request, said method comprising steps of:said subscriber terminal sending an information distribution transmission request including at least information for identifying said subscriber terminal sending said request, information for identifying said requested information, and urgency information relating to an urgency level of said requested information, said urgency information including a real time transmission request; said information distribution transmission center planning a transmission schedule of said requested information to be transmitted based on said information distribution transmission request from said subscriber terminal, and transmitting said planned transmission schedule to said subscriber terminal which requested said information distribution transmission request in down-going control data prior to transmission of said requested information, and transmitting said requested information according to said planned transmission schedule; said information distribution transmission center allocating a plurality of transmission channels for use for a plurality of urgency levels, wherein a number of said plurality of transmission channels allocated for a high urgency level increases in accordance with an increase in a number of requests for information distribution transmission; and said subscriber terminal receiving said transmission plan and analyzing said down-going control data from said information distribution transmission center, acquiring said requested information transmitted from said information distribution transmission center based on said transmission plan, storing said acquired information in memory means having a large capacity when said urgency information is other than a real time transmission request, and providing said information read from said memory means for use, wherein when said urgency information is a real time transmission request said acquired information is supplied for use without being stored in said memory means.
 8. The method of two-way information transmission as claimed in claim 7, wherein said information distribution transmission center transmits in real time in response to said real time transmission request which requests immediate transmission included in said information distribution transmission request from said subscriber terminal, and transmits in a free channel of an available time zone when said urgency information allows for a time delay before transmission.
 9. The method of two-way information transmission as claimed in claim 7, whereinsaid urgency information included in said information distribution transmission request specifies any one of said plurality of urgency levels each having a different delay time from a distribution transmission request to transmission of said requested information, and a communication capacity of said down-going line is allocated and assigned separately for each urgency level of said plurality of urgency levels.
 10. The method of two-way information transmission as claimed in claim 9, wherein said communication capacity assigned to each urgency level is variable depending on a transmission time zone and day of a week.
 11. A subscriber terminal of a plurality of subscriber terminals respectively connected to an information distribution transmission center through up-going lines and down-going lines, in which said subscriber terminal requests transmission of information from said information distribution transmission center through said up-going line, and said information distribution transmission center transmits said requested information through a down-going line in response to said request for transmission of information, said subscriber terminal comprising:distribution transmission request sending means for sending an information distribution transmission request including at least information for identifying said subscriber terminal making said request, information for identifying information requested for transmission, and urgency information relating to an urgency level of said requested information, said urgency information including a real time transmission request; memory means; transmission plan receiving analysis means for acquiring a transmission plan of information to be transmitted, said transmission plan being planned by said information distribution transmission center based on said information distribution transmission request from said subscriber terminal, by referring to control data sent from said information distribution transmission center; information acquisition means for acquiring said requested information transmitted from said information distribution transmission center and storing said acquired information in said memory means when said urgency information is other than a real time transmission request based on said transmission plan acquired by said transmission plan receiving analysis means, wherein when said urgency information is a real time transmission request said acquired information is supplied for use without being stored in said memory means; and reading means for reading information from said memory means, wherein said information distribution transmission center allocates a plurality of transmission channels for use for a plurality of urgency levels such that a number of said plurality of transmission channels allocated for a high urgency level increases in accordance with an increase in a number of requests for information distribution transmission. 